<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>position</title>
<style>
	div{
			width: 100px;
			height: 100px;
			font-size: 30px;
			text-align: center;
			line-height: 100px;
		}
		.box1{
			background-color: pink;

		}
		.box2{
			background-color: skyblue;
			position:absolute;
			left:50px;
			top:100px;
			z-index: -1;
		}
		.box3{
			background-color: yellowgreen;
		}
		.container{
			width: 500px;
			height: 500px;
			background-color: #ccc;
			margin:0 auto;
			position:relative;
			z-index: -2;
		}
</style>
</head>
<body>
	<div class="container">
		<div class="box1">box1</div>
		<div class="box2">box2</div>
		<div class="box3">box3</div>
	</div>
</body>
</html>